With my castles I start running out of space quickly and some of the houses don't have much outdoors space for items to begin with. Using the Acropolis as an example, there are mulitple floating islands. One is for the arena, another is for a small empty plot of land.
My suggestion would be to add a housing item to the crowns shop which adds a floating island of land to your home. These would come in small medium, and large sizes and in a variety of terrain (grassy, snowy, desert, paved). Like teleporters, this would count as one item towards your limit but would each have a bonus block total (50 for small, 100 for medium, 150 for large) to allow for castle block building.
The housing item would be the round teleporter disk that you step on plus the island. Step one you place the disk near an edge. Step two you place the island with a linked disk "offshore" in empty air. Boom! Now your home is bigger and you have empty land available to upgrade your estate.
Why have these? 1. With castle building and crafting, we need empty land to build on. I have Midday Estate but would love to have buildings on other homes as well.
2. Garden islands
3. Arena islands for PVP kiosks
4. Separate dungeon islands for your Winterbane, Midnight Pagoda, Fishing Retreat, etc.
5. More room to be creative and build a maze or an island for all of your teleporters or just to surround your home with huge zebra statues.
6. Room to grow for people who love their small homes but have no more room and don't want to buy another house but would spend crowns
